The present invention concerns the control of the damping of tires of one or more axles of a vehicle provided with at least two tires, mounted on handling machines such as lift trucks, cranes or loaders used for civil engineering work.
The use of tires which are filled with gas under pressure on forklift trucks in replacement of solid tires has been crowned with success. However, it still raises certain problems which have been poorly solved up to the present time. These problems are due essentially to, at times, insufficient stability of the truck when the forks are in raised position up to several meters in height lifting or taking on a load.
In this configuration, and in similar cases observed with loaders or cranes, the flexibility and elasticity of the tires, combined with the distance at which the load is handled, transforms each movement of the vehicle or the load (particularly in the event of variation of force applying essentially to the load, the vehicle being at rest, or to the entire vehicle in movement due to the irregularities in travel) into a series of front to rear, left to right oscillations which are at times dangerous since there may be the risk of the toppling over of the vehicle. At the very least, these oscillations are extremely disturbing for the maneuvers of positioning the load. It is to be noted that these oscillations are of greater concern the more flexible and elastic that the tires are.
These parasitic movements could, of course, be limited if the vehicle were driven without abruptness, but then the overall efficiency might suffer. Moreover, these machines do not always have controls which are sufficiently gradual to be able to limit the undesirable oscillations or the means for damping them effectively.
It is already known to increase the stiffness of the tires used for handling applications either by filling them with polyurethane or with an incompressible material such as water, or by using reinforced inner tubes.
These solutions come down to transforming the tire in order to impart to it characteristics of stiffness which approach those of a solid tire, either permanently or intermittently as in the case of patent FR2657819. When the tire acquires the behavior of a solid tire due to these solutions, a significant increase in the load supported, due for instance to a transfer of load, is accompanied by a much smaller change in the vertical deformation of the tire, that is to say its sag, than in the case of a purely pneumatic tire, which greatly limits the amplitude of the oscillations caused by the transfer of load. On the other hand, the damping of these oscillations by the wheel or wheels is not always sufficient, due to the large residual elasticity of each liquid-filled pneumatic wheel.
The solution recommended in Japanese Patent Application No. 3-284401 proposes establishing a connection between the inside of each liquid-filled tire and an accumulator adapted to receive a certain amount of this liquid coming from one of the tires subjected to an additional force of dynamic compression due to jolts upon travel. The accumulator returns the liquid to the tire, which resumes its normal configuration via a restrictor bringing losses of head into the sole return flow of this liquid, in order to contribute a dampening of the vibrations. The diaphragm accumulator used makes it possible to limit the sudden variations in pressure, by maintaining the pressure at the level of pressure of the pressurized gas of the accumulator, permitting variations in volume and sag of the tire subjected to an addition force, which confers upon it less stiffness than if it had remained isolated and therefore full with a constant volume of liquid. The connections described place each liquid-filled tire in communication with the accumulator, these tires being also connected to each other, but without there being a direct transfer of liquid from one to the other, since the liquid is evacuated into the accumulator. It can therefore be noted that the volume of liquid within the system of connections between the tires is not constant due to the role of the accumulator. It will furthermore be noted that the damping of the vibrations by loss of head in the flow of the liquid takes place only in a single direction of movement of flow of the liquid. The use of such an arrangement causes the liquid-filled tire to lose the advantage of its very great stiffness, which generates vibrations of greater amplitude, with a limited capacity for the damping thereof.